1. Field of the Invention (Technical Field)
The present invention relates to an exhaust gas cooler component of an exhaust gas recirculation (EGR) system for an internal combustion engine, and more particularly to an exhaust gas cooler with an internal bypass, and optionally with a concentric flow gas intake manifold and valve mechanism.
2. Description of Related Art
EGR systems recirculate at least a portion of the engine exhaust gases into the engine air intake system for the purpose of reducing NOx emissions. Exhaust gas coolers are used to cool a portion of the exhaust gas. Typical prior art exhaust gas coolers are cylindrical shells that define a coolant chamber within the shell. In one prior art embodiment, the engine coolant is caused to flow through the shell, thereby providing a coolant liquid for use in heat exchange. A plurality of small diameter gas cooling passages, such as tubes, transit the length of shell, with each such passage surrounded by the coolant liquid. Thus the exhaust gas is directed through the plurality of small diameter gas cooling passages, and a portion of the heat of the exhaust gas is transferred to the coolant liquid during passage of the exhaust gas through the exhaust gas cooler. The cylindrical shell defining the exhaust gas cooler may have a circular tube plate at each end, sealing the cylindrical tube. The circular tube plates may further have a plurality of holes for receiving, at each end, the plurality of small diameter exhaust gas passages.
As emissions regulations become more stringent, one of the methods of maintaining compliance is to use a bypass exhaust gas cooler which can vary cooling performance depending upon system requirements. For example, at certain times, such as during engine start-up, it is preferable to stop the exhaust gases from being cooled. It is known to utilize an exhaust gas cooler with a separate bypass tube external to the exhaust gas cooler, typically with a valve arrangement, so that exhaust gases can be diverted around the exhaust gas cooler when cooling is not required. This provides a cooling circuit, in which exhaust gas is cooled, and a bypass circuit, in which exhaust gas is not cooled. However, use of a separate bypass tube external to the exhaust gas cooler adds a bulky component to the engine compartment. Particularly with the frequently cramped layout of the engine compartment of a road vehicle, space is at a premium and thus adding a separate bypass tube is not desirable. Additionally, because of the differential rates of expansion and contraction of the exhaust gas cooler and the separate bypass tube during operation, it is necessary to include an expansion means, such as a bellows, to the external bypass tube. This adds to the complexity of construction, adds additional cost, and provides a component that is subject to failure.
It is also known to employ an exhaust gas cooler which diverts all or a portion of the exhaust gas prior to delivery of the exhaust gas to the exhaust gas cooler. For example, one such device employs an exhaust gas cooler which, rather than a cylindrical shell in which gas transits the length of the shell and exits from the end opposite the entrance, has the exhaust gas entrance and exhaust gas exit on the same end, with the exhaust gas reversing direction within the exhaust gas cooler. However, this type of exhaust gas cooler is frequently more bulky than other forms of exhaust gas coolers in which the exhaust gas entrance and exit are on opposite ends. Additionally, this type of exhaust gas cooler requires a redesign of the exhaust gas flow circuit within the engine compartment, is not readily amenable to retrofitting existing engines, and can require significant modifications to engine layouts.
It is advantageous to have an exhaust gas cooler which can be employed such that all exhaust gas is cooled, no exhaust gas is cooled, or only a portion of the exhaust is cooled. Thus in order to provide optimal performance it is advantageous to have an exhaust gas cooler in which not only can the bypass circuit be opened, but also the cooling circuit can be simultaneously physically closed, thereby preventing any exhaust gas cooling in the event that all exhaust gas is diverted to the bypass circuit.
In typical exhaust gas coolers with some form of bypass, the valve assembly for directing exhaust gas to either the cooler circuit or the bypass circuit is an integral part of the exhaust gas cooler or a manifold connected to the exhaust gas cooler. Typically valve components are the only moving parts within the exhaust gas cooler circuit, and include components which are welded or brazed. Because the valve components are movable and actuated by some form of actuator, the components are prone to mechanical failure. However, because of the design of typical exhaust gas coolers, either the entire exhaust gas cooler, or alternatively a manifold or similar component, must be replaced in the event of failure of the valve components. This design adds to costs of construction, since welding or brazing must be performed on a relatively large component, and further increases costs of maintenance, since large components must be replaced in the event of failure of a relatively small sub-component.